Embodiments described herein relate to a system and method for injecting an emission liquid reductant into a gas stream, and more particularly, to a system and method for injecting ammonia into an exhaust gas stream of a diesel engine.
Diesel engine combustion results in the formation of nitrogen oxides, (NOx), in the exhaust gas. Aftertreatment systems, typically selective catalytic reduction systems (SCR systems) are used to reduce oxides of Nitrogen (NOx) emitted from engines. Nitrogen oxides can be reduced by ammonia (NH3), yielding N2, H2O and C02. In the aftertreatment process, NOx reacts with the ammonia, which is injected into the exhaust gas stream upstream of an SCR Catalyst.
The aftertreatment process requires control of the ammonia injecting rate. An insufficient injection may result in low NOx conversions, and an injection rate that is too high may result in release of ammonia to the atmosphere, known as ammonia slip. The ammonia slip increases at higher NH3/NOx ratios. The ammonia injection depends on the injection characteristics and the energy of the exhaust gas. If the ammonia is improperly dosed with respect to the amount, the timing, the temperature, the space velocity, the current storage level and the NOx mass flow, ammonia slippage may result.